Flotation machine

ABSTRACT

The invention relates to a flotation machine which at least contains a flotation cell having a means for feeding slurry in the flotation cell, a means for feeding air into the slurry and producing froth, a means for removing froth from the flotation cell and a means for removing tailings from the flotation cell. According to the invention the flotation cell ( 1,21 ) is provided with at least one rotating froth removal device ( 8,26 ) immersed at least partly in the froth ( 9,27 ) and so shaped that one end of the froth removal device ( 8,26 ) is extendible over the launder ( 12 ) attached to the flotation cell ( 1 ) in order to recover the froth ( 9,27 ) from the flotation cell ( 1,21 ) using the centrifugal force generated by the froth removal device ( 8,26 ).

The invention relates to a froth flotation machine to be used inflotation of slurry for separation valuable components from tailings, inwhich machine a device is installed in the upper part of the cell frothzone so that at least one part of the rotating device is partly immersedinto the froth in order to improve the removal of froth from theflotation machine.

A froth flotation machine for recovering valuable mineral particlesnormally comprises a flotation cell in the form of a tank having aninlet in the cell wall for feeding slurry to be flotated as well as anoutlet for tailings in the lower part of the cell. Air for generating afroth is fed through a hollow and rotatable shaft which is connected toan agitator that mixes the slurry to keep it in suspension. As theagitator rotates air is fed into the slurry and bubbles are dispersed.Suitable reagents are also added to the process which reagents arecapable of coating the surfaces of valuable mineral particles to maketheir surfaces hydrophobic and so promote bubble/particle attachment.Once the valuable mineral particles attach to an air bubble they slowlyrise to the cell surface to form a stable froth zone. This froth layeris mobile and travels across the cell surface and is collected into aconcentrate launder which often surrounds the upper part of theflotation cell. When the cell size is increased the distance between thecentre part of the flotation cell and the concentrate launder will alsoincrease. This means that the removal of froth from the flotation cellis not very effective since a longer transport distance means that theprobability of bubble coalescence and particle drop back will increase.Therefore, different devices are installed in the flotation cell foreffecting the removal of froth.

The U.S. Pat. No. 5,039,400 describes a regulating member for frothcreated in a flotation machine. This regulating member is a cone whichtop is immersed in the froth. Thus the free area of froth is upwardsdecreased and the froth is obliged to go closer and closer to the wallof the flotation cell and thus closer to the concentrate laundersurrounding the upper part of the flotation cell.

The U.S. Pat. No. 4,913,805 relates to an apparatus and method for frothflotation separation of the components of a slurry, having particularutility for the beneficiation of coal. In this arrangement a spraynozzle is positioned above a flotation tank and the spraying operationcreates a froth on the water surface. For the removal of the frothcontaining a substantial quantity of coal particles a continuouslyoperating skimming arrangement having ridges or ribs skims the frothfrom the water surface as a cleaned or beneficiated product.

The skimming arrangement as described in the U.S. Pat. No. 4,913,805 ispractical in a flotation tank which has a launder for froth only on thatarea where the skimming arrangement moves froth from the centre part ofthe concentrate tank towards that part of the lip which is provided withthe launder.

The regulating member of the U.S. Pat. No. 5,039,400 decreases thedistance from the centre part of the flotation cell to the lip of theflotation cell. Further, the regulating member can be used with aconcentrate launder surrounding the flotation cell and thus froth can beremoved from the flotation cell freely independent on the directionstowards the concentrate lip of the flotation cell. While this regulatingmember is effective for reducing froth transport distance it becomesless effective as the cell size increases above 50 cubic meters. Thenett active volume of the flotation cell is also significantly reducedby the regulating member as the cell size increases.

The object of the present invention is to eliminate some drawbacks ofthe prior art and to achieve a device for effecting the removal of frothfrom the free area in the upper part of a flotation machine. Theessential features of the invention are enlisted in the appended claims.

According to the invention at least one device for improving the removalof froth essentially from the whole free area of froth is installed inthe upper part of a flotation machine which at least contains aflotation cell having a means for feeding slurry in the flotation cell,a means for producing froth, a means for removing froth from theflotation cell and a means for removing tailings from the flotationcell. The device for improving the removal of froth is installed so thatthe device is partly immersed below the surface of froth. The frothremoval device is operated by a drive mechanism, and when the frothremoval device is in operation, the froth produced onto the surface ofthe flotation cell is removed from the cell without the need for thefroth concentrate to travel horizontally to be recovered to a launderhaving a connection with a lip of the flotation cell. This is becausethe froth removal device is shaped so that when operating the devicewill remove the froth at a predetermined height.

The froth removal device of the invention has a cutting face which ispartly immersed below the surface of the froth at a predeterminedheight. The cutting face will cut the froth surface in an inclined orhorizontal position to the froth surface so that at least most of thefroth bubbles within the froth zone are not broken or caused tocollapse. The bubbles contain on their surface the valuable componentswhich will form at least one portion of a froth concentrate recoveredfrom the flotation cell. The bubbles cut from the froth will slide alongthe surface of the froth removal device into a froth removal member ofthe device connecting to the cutting face. The froth removal member isinstalled so that the lower surface of the froth removal device isessentially at the same level as the upper part of the lip between thelaunder and the froth zone. This means that the centrifugal forcegenerated as the froth removal device rotates forces the froth up theinclined cutting face. Once the froth reaches the lower surface of therotating froth removal member the bubbles in the froth at least partlyare deaerated and thus broken back to a slurry and the slurry will flowin the froth removal member towards the lip of the flotation cell andfurther into the launder surrounding the flotation cell.

When using the froth removal device of the invention it is advantageousto provide the flotation cell with froth stabilising members. The frothstabilising members are located within an essentially even distance fromeach other so that plural froth stabilising members are operated in theessentially whole free froth area of the flotation cell. The number ofthe froth stabilising members is advantageously at least eight and thefroth stabilising members are installed in the froth zone close to thefroth removal device in order to prevent a possible froth collapseduring the movement of the froth removal device. This froth collapse iscaused by a slight vacuum behind the froth removal device when the frothremoval device moves across the froth surface.

By using the froth removal device of the invention the amount of theparticle drop back into the pulp phase is essentially reduced andthereby the recovery of valuable components is increased overall and ata much faster rate than in the prior art. Further, the froth removaldevice of the invention will allow the amount of the lip length requiredin a flotation cell to be varied by changing both the number of thedevices and the operating speed compared with the lip. Hence, it is alsoto control the rate of removal of the froth concentrate and thereby itsgrade.

The froth removal device of the invention will help to improveespecially the recovery of coarse particles from a flotation cellbecause the froth removal device will limit the time a coarse particleneeds to spend in the froth phase before being removed to the launder.The froth removal device will eliminate the need for complicatedinternal launders and will also reduce the amount of crowding of thefroth free area required.

Because the froth removal device will at least partly deaerate therecovered froth concentrate the size of a perimeter launder will bedecreased. Also subsequent piping is to be substantially decreased insize without limiting the performance.

The invention is described in more details in the following drawingswhere

FIG. 1 shows one advantageous embodiment of the invention as aschematical and partial cross-sectional side view,

FIG. 2 shows a section A—A of the embodiment FIG. 1 schematically as anenlarged view, and

FIG. 3 shows another advantageous embodiment of the invention as aschematical and partial cross-sectional side view.

In FIG. 1 a flotation cell 1 has in the wall an opening 2 for slurry tobe flotated as well as a launder 3 for froth concentrate produced in thecell 1 is attached to the wall. The flotation cell 1 has in the bottompart an opening 4 for tailings. The flotation cell 1 has also in itslower part a rotor 5 surrounded by a stator 6. The rotor 5 is attachedto an axis 7 which is rotated by a motor 17. The axis 7 is hollow andair for froth flotation is fed through the hollow axis 7 to the rotor 5.The froth removal device 8 is installed coaxially but separately withthe axis 7 in the upper part of the flotation cell 1 in the height wherethe froth removal device 8 is at least partly immersed in the froth 9produced in the flotation cell 1. Froth stabilising members 18 areinstalled in the froth 9 below the froth removal device 8 radially froma froth regulating member 13 towards the wall of the flotation cell 1.

The froth removal device 8 is operated by a drive mechanism 10. The end11 of the froth removal device 8 separated from the axis 7 is shaped sothat the end 11 of the froth removal device 8 will extend over the lip12 between the launder 3 and the froth zone in the flotation cell 1. Inthe flotation cell 1 a froth regulating member 13 is surrounding theaxis 7. The froth removal device 8 is installed so that essentially thewhole free froth area is accessible for the froth removal device 8 whenoperated.

FIG. 2 shows the froth removal device 8 in more details. The cuttingface 14 is at least partly immersed in the froth 9 containing bubbles 15to be removed. The cutting face 14 is in an inclined position to thebubbles 15 so that at least most of the bubbles 15 are unbroken whenremoved from the froth 9 to the surface of the cutting face 14 andfurther to the lower surface of the froth removal member 16 of the frothremoval device 8. The froth removal member 16 is so installed that thelower surface of the froth removal member receiving the froth isessentially at the level as the lip 12 between the launder 3 and thefroth zone in the flotation cell 1. In the froth removal member 16 ofthe froth removal device 8 the bubbles 15 are deaerated and thus broken.Froth as liquid form flows towards the launder 3 and thus out of theflotation cell 1.

The embodiment of the FIGS. 1 and 2 will be operated so the frothremoval device 8 is rotated coaxially with the axis 7 by the drivemechanism 10. When rotating the centrifugal force will pump thedeaerated froth in the froth removal device 8 towards the launder 3 andthus out of the flotation cell 1.

In FIG. 3 a flotation cell 21 is provided with an inlet 22 for slurryand a launder 23 for froth and an outlet 24 for tailings. There is alsoa means 25 for supplying air into the flotation cell 21. A froth removaldevice 26 is installed on the froth zone 27 so that a cutting face 28 ofthe froth removal device 26 is partly immersed into the froth 27. Thefroth removal device 26 is rotated by a drive mechanism 29. Further,froth stabilising members 30 are installed below the cutting face 28into the froth zone 27. The operation and the structure of the frothremoval device 26 is similar to the froth removal device of theembodiment in FIG. 1. This means that when rotating the centrifugalforce will pump the deaerated froth in the froth removal device 26towards the launder 23 and thus out of the flotation cell 21.

1. Flotation machine comprising: a flotation cell having a means forfeeding slurry in the flotation cell, a means for feeding air into theslurry and producing froth, a means for removing froth from theflotation cell, a means for removing tailings from the flotation cell,means for preventing a possible froth collapse during movement of thefroth removal device consisting essentially of at least eight evenlyspaced, radially oriented stabilizing members; and at least one rotatingfroth removal device, which is capable of being at least partly immersedin the froth, the froth removal device having a portion that extendsover a launder, capable of carrying froth into the launder, the frothremoval device being attached to the flotation cell, for recovery offroth, the froth removal device capable of generating centrifugal force,that causes froth to travel from the flotation cell, along a face of thefroth removal device, to the launder, and at least eight frothstabilizing members for preventing a possible froth collapse duringmovement of the froth removal device.
 2. Flotation machine according toclaim 1, wherein the froth removal device is provided with a cuttingface partly immersed in the froth.
 3. Flotation machine according toclaim 1, wherein the froth removal device is provided with a cuttingface installed in an inclined position relative to an upper surface ofthe froth.
 4. Flotation machine according to the claim 1, wherein thefroth removal device is provided with a cutting face installed in ahorizontal position relative to an upper surface of the froth. 5.Flotation machine according to claim 1, wherein the froth removal deviceis provided with a froth removal member in order to remove materialattached to the froth from the flotation cell.
 6. Flotation machineaccording to claim 1, wherein the froth removal device is installedcoaxially with a slurry rotating member.
 7. Flotation machine accordingto claim 1, wherein the froth removal device is operated with a drivemechanism separated from a motor rotating the slurry rotating member. 8.Flotation machine according to claim 1, wherein the froth removal deviceoperates over substantially a whole free froth area of the flotationcell.